As someone with too many gallery walls I’m so glad you asked

A couple ideas:

Thrift and pretty-up your finds with paint, fabric, your own DIY mats. I love the look of over-sized mats in a frame, or a monochromatic mat painted same color as the frame, or fabrics decoupaged onto the mat and/or frame!

Or if you’re going for a uniform look / less DIY, Michaels has shockingly good sales sometimes - SPECIFICALLY, periodically they do a “buy one get two free” on their in-house brand called “studio decor.” Search Michael’s site for frame with mat studio decor 💗 plot twist - the sale is on now. Meant to be?